1. Field of the Invention
The present invention relates to a shading correction method for a heat development recording apparatus in which a heat development recording material is exposed to a laser beam, and then, the heat development recording material is thermally developed and a heat development recording apparatus.
2. Description of the Related Art
In recent years, the amount of processed waste liquid has been eagerly requested to decrease from the viewpoints of environmental protection and space saving in a medical field. Thus, a technique concerning photosensitive and heat development photographic materials utilized for a medical diagnosis and a usage of photographic technique which can be efficiently exposed by a laser image setter or a laser imager and can form a clear black image having a high resolution and a sharpness has been required. These photosensitive heat development recording materials allow the use of solution type processing chemicals to be eliminated and a simpler heat development processing system which does not degrade an environment to be supplied to customers.
The same requests are likewise present in the field of ordinary image forming materials. However, since a medical image needs a fine description, the image needs a high image quality excellent in its sharpness and graininess. In addition, a cold black-tone image is characteristically preferable in view of easiness for diagnosis. Although various kinds of hard copy systems using pigments and dyes such as ink jet printers, electro-photography, etc. are currently distributed as ordinary image forming systems, they are not satisfactory as output systems of medical images.
As compared therewith, in recent years, a recording apparatus based on a dry system in which a wet process is not carried out has been paid attention to. In such a recording apparatus, a film composed of a photosensitive and heat sensitive recording material (photosensitive heat sensitive recording material) or a heat development photosensitive material is employed. The material is referred to as a “heat development recording material” or a “heat development photosensitive material”, hereinafter. In the recording apparatus based on the dry system, the heat development recording material is irradiated with a laser beam (scanned) in an exposure unit to form a latent image. Then, the heat development recording material is allowed to come into contact with heating means to perform a heat development in a heat development unit. Then, the heat development recording material is cooled to deliver outside the heat development recording material on which an image is formed. The dry system can solve a problem of waste liquid treatment as compared with the wet process.
A heat image system using organic silver salt as described above is disclosed in, for instance, the specifications of U.S. Pat. Nos. 3,152,904 and 3,457,075 and “Thermally Processed Silver Systems” by B. Shely (Imaging Processes and Materials; the eighth edition of Neblette edited by Sturge, V, Walworth and A. Shepp, P2, 1996). Especially, the heat development recording material has a photosensitive layer in which a photo-catalyst having a catalytic activation amount (for example, halogenated silver), a reducing agent, reducible silver salt (for example, organic silver salt) and a color tone agent for controlling the color tone of silver as required are dispersed in the matrix of a binder. The heat development recording material is heated to high temperature (for instance, 80° C. or higher) after the exposure of an image. Then, a black silver image is formed by an oxidation-reduction reaction between the halogenated silver or reducible silver salt (functions as an oxidizing agent) and the reducing agent. The oxidation-reduction reaction is accelerated by the catalytic action of the latent image of the halogenated silver generated by the exposure. Therefore, the black silver image is formed in an exposure area. Fuji Medical Dry Measure FM-DPL was disclosed in many documents such as U.S. Pat. No. 2,910,377 and JP-B-43-4924 and then sold as a medical image forming system by using a heat development recording material.
In a production of the heat image forming system using the organic silver salt, a method for producing the system by applying a solvent and a method for producing the system by applying and drying application liquid containing polymer micro particles dispersed in water as a main binder are included. The latter method does not need a step of recovering the solvent, so that a production facility is simple and advantageous for a mass-production.
In such a heat development type image recording, even when a record having uniform density is carried out, what is called shading that unevenness in recording density is generated in a main scanning direction is caused due to the characteristics of the recording apparatus itself. Accordingly, the quality of a recorded image is inconveniently deteriorated. Causes thereof may possibly include unevenness in reflection factor of a polygon mirror scanned by laser beam for exposure, unevenness in transmission factor of a lens or unevenness in temperature of a heat development unit or the like.
In order to prevent the quality of an image due to the above-described shading, what is called a shading correction that the unevenness in the recording density due to shading is corrected is carried out. This shading correction is disclosed in, for example, JP-A-11-38517 and performed as described below. Firstly, a recording operation by the image data of uniform density in the main scanning direction is performed and the density of the recorded image is continuously measured along the main scanning direction by a desitometer incorporated in the recording apparatus. Then, shading correction data (correcting conditions) that the recording density distribution for all pixels is uniform is calculated for each pixel and a shading correction table is formed by collecting together the shading correction data corresponding to each pixel. Upon actually recording an image, image data supplied from an image data supply source is corrected for each pixel by using the shading correction data read from the shading correction table to carry out the shading correction.
In the above-described recording apparatus, in order to carry out the above-described shading correction, a recording density measuring unit for continuously measuring the recording density of a recorded image in a main scanning direction has been incorporated in the recording apparatus. This recording density measuring unit comprises a light source for uniformly applying light to a recording medium along a main scanning direction and a photoreceptor for detecting the light reflected on the surface of the recording medium which is irradiated with the light from the light source along the main scanning direction. The recording density measuring unit is highly accurate and expensive.
A user side that uses the recording apparatus also needs such a shading correction to be periodically carried out. When the shading correction is carried out only once in the density measuring unit before the recording apparatus is shipped, so much unevenness in recording density is not generated after that.
Accordingly, for the purpose of the shading correction after shipping that rarely needs accuracy, the incorporation of the highly accurate and expensive density measuring unit inconveniently causes much wastefulness and does not achieve low cost.